[vsnet-grb-info 23540] LIGO/Virgo S190901ap: Keck I LRIS spectroscopy of ZTF19abvizsw

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25639
SUBJECT: LIGO/Virgo S190901ap: Keck I LRIS spectroscopy of ZTF19abvizsw
DATE:    19/09/04 00:27:15 GMT
FROM:    Mansi M. Kasliwal at Caltech/Carnegie  <mansikasliwal at gmail.com>

Kevin Burdge (Caltech), Daniel A. Perley (LJMU) and Mansi M. Kasliwal
(Caltech) report on behalf of the GROWTH collaboration:

We obtained a Keck I LRIS spectrum of ZTF19abvizsw (Kool et al. GCN
25616).  The reduced spectrum shows a featureless continuum superimposed
with a number of narrow absorption lines, including Mg II, Mg I, and Fe II
at a consistent redshift of z=1.26.

This is far beyond the GW distance constraints on S190901ap (LVC et al. GCN
25614, GCN 25606) and demonstrates that this source is unrelated to the
LIGO/Virgo source.  It could be a flaring AGN or blazar, but there is no
counterpart in PS1 or WISE and only a dim, marginal object at this location
in the Legacy Survey.  It may also be a GRB afterglow.

Our conclusions disagree with those of Salmaso et al. (GCN 25618), who
reported an M- or K-dwarf spectrum for this object.  We note that there is
a bright, red star less than 2 arcsec away from the transient position and
it is possible that the spectrum reported in GCN 25618 may correspond to
that object.